Several studies have shown that a large proportion of patients with major depressive disorders exhibit hyperactivity of the hypothalamic-pituitary- adrenal (HPA) axis function, expressed by elevated plasma cortisol concentrations. We hypothesize that young children with behavior problems, particularly those who show concurrent symptoms of depression and anxiety, may have hyperactivity of HPA axis function, as indicated by elevated plasma and salivary cortisol levels. Approximately 80 behavior problem children, aged 6-7 years, received a physical examination in order to get extensive pediatric history (perinatal, developmental and general medical history); in addition, plasma ACTH and plasma and salivary cortisol levels were assessed. This provides the opportunity to evaluate the HPA axis function in these children, to evaluate the correlation between plasma and salivary cortisol levels, and to assess cortisol response under stress and nonstress conditions. Such information would be useful for distinguishing between possible sub-types of disruptive behavior disorders in early childhood.